What is considered a notable event in the context of Splunk ES?

In Splunk Enterprise Security (ES), a notable event is defined as an event that has been flagged for investigation due to its potential significance or abnormality, often reflecting a security concern. These events are typically identified through alerts that are generated based on specific criteria established by security policies or protocols. The purpose of categorizing certain events as notable is to allow security analysts to prioritize which incidents require further investigation, thus enhancing a security team's ability to respond effectively to potential threats.

Events such as ordinary log entries do not hold the same level of urgency or importance as notable events, as they might not indicate any suspicious behavior. Similarly, scheduled maintenance alerts are related to system upkeep rather than security issues. While a user login attempt could potentially be a notable event, it is not inherently categorized as such without the context of its behavior, such as failing multiple times or occurring at odd hours, which would raise suspicion and lead to it being flagged for investigation.

Therefore, a notable event represents a specific trigger or condition that necessitates further scrutiny, which is why the correct choice is the event that is flagged for investigation.